概要 Each of these monolithic circuits contains eight master-slave flip-flops and additional gating to implement two individual four-bit counters in a single package. The '390 and 'LS390 incorporate dual divide-by-two and divide-by-five counters, which can be used to implement cycle lengths equal to any whole and/or cumulative multiples of 2 and/or 5 up to divide-by-100. When connected as a bi-quinary counter, the separate divide-by-two circuit can be used to provide symmetry （a square wave） at the final output stage. The '393 and 'LS393 each comprise two independent four-bit binary counters each having a clear and a clock input. N-bit binary counters can be implemented with each package providing the capability of divide-by-256. The '390, 'LS390, '393, and 'LS393 have parallel outputs from each counter stage so that any submultiple of the input count frequency is available for system-timing signals. Series 54 and Series 54LS circuits are characterized for operation over the full military temperature range of -55°C to 125°C; Series 74 and Series 74LS circuits are characterized for operation from 0°C to 70°C.
特長 Dual Versions of the Popular '90A, 'LS90 and '93A, 'LS93 '390, 'LS390 … Individual Clocks for A and B Flip-Flops Provide Dual ÷ 2 and ÷ 5 Counters '393, 'LS393 … Dual 4-Bit Binary Counter with Individual Clocks All Have Direct Clear for Each 4-Bit Counter Dual 4-Bit Versions Can Significantly Improve System Densities by Reducing Counter Package Count by 50％ Typical Maximum Count Frequency … 35 MHz Buffered Outputs Reduce Possibility of Collector Commutation
